Teadusartiklid / Research articles 29
Agraarteadus
1 * XXIX * 2018 29–40
Journal of Agricultural Science
1 * XXIX * 2018 29–40
COMPARATIVE ASSESSMENT OF SELECTED HEAVY METAL
LOAD IN THREE TILAPIINE SPECIES INHABITING OSINMO
RESERVOIR, SOUTHWESTERN NIGERIA
Ayomide Omolara Olofinko1, Henry Adefisayo Adewole2, Victor Folorunso Olaleye2
1Institute of Ecology and Environmental Studies, Obafemi Awolowo University, Ile-Ife, Nigeria 2Department of Zoology, Obafemi Awolowo University, Ile-Ife, Nigeria
Saabunud: 30.11.2017
Received:
Aktsepteeritud: 12.06.2018
Accepted:
Avaldatud veebis: 12.06.2018
Published online:
Vastutav autor: Henry
Adefisayo
Adewole
Corresponding author:
E-mail:
Keywords: heavy metal, tilapiine,
Osinmo reservoir, fillet, health, safety,
consumption.
doi: 10.15159/jas.18.05
ABSTRACT. The levels of selected heavy metal in the water and fillets
of Tilapia zillii Gervais, Sarotherodon galilaeus Trewavas and
Oreochromis niloticus Lineaus in Osinmo Reservoir were assessed and
compared with established regulatory limits of WHO and FEPA with a
view to providing information on the water and the fish fillet heavy
metal load as well as the fillet bio-accumulative potential as a likely
indicator for human fish consumption safety. Water samples and fish
specimens were collected monthly from Osinmo Reservoir, Ejigbo,
Southwestern Nigeria for a period of 6 months. The descaled-dried fish
fillet and water samples were digested and analysed for lead, chromium,
iron, zinc and cadmium using Atomic Absorption Spectrophotometer
(A.A.S.). The data obtained were subjected to descriptive and inferential
statistics using SPSS 21. The results showed that zinc concentration
which was the highest in the water samples and ranged between
144 µg l-1 and 288 µg l-1 was also the highest in the fillets of all the
cichlid species. However, the concentrations were within the mandatory
regulatory limits. The result of the study also revealed significant
differences (P < 0.05) in heavy metal loads of the fish fillets between the
cichlid fish species from Osinmo Reservoir. Irrespective of the month
of sampling, the heavy metal levels in fish fillets samples were found to
increase in the order: O. niloticus > T. zillii > S. galilaeus. However, the
levels of lead (11.00–26.00 µg l-1 and 15.00–31.00 µgL-1) and cadmium
(6.33–13.00 µg l-1 and 2.33–12.33 µg l-1) which was the least in both
water and fish fillet respectively, were above the recommended
regulatory acceptable limit of WHO and FEPA. The study concluded
that the elevated levels of lead and cadmium in the water and the fish
fillet samples assayed indicated that the two elements negatively
impacted the fish fillet quality, thereby raising human health
consumption safety issues.
© 2018 Akadeemiline Põllumajanduse Selts. Kõik õigused kaitstud. 2018 Estonian Academic Agricultural Society. All rights reserved.
Introduction
The steady increase in the industrial revolution has
led to the increase in the pollution of the aquatic
environment especially with heavy metals which are
indestructible and most of which have toxic effects on
organisms (MacFarlane, Burchett, 2000). Apart from
the industrial revolution, human activities have been
associated with increase in the concentration of metals
in many of the natural water systems which have raised
concerns regarding metal bio-accumulation and human
health hazards (Ekpo et al., 2013). Documented sources
of how heavy metals enter aquatic systems from natural
sources and other anthropogenic activities include
industrial or domestic sewage that contain sediments
with huge quantities of inorganic anions and heavy
metals (ECDG, 2002; Ekpo et al., 2013), leaching from
landfills/dumpsites, atmospheric deposits, and run-offs
from agricultural land and drainage water which have
been reported to contain pesticides and fertilizers
(Edem et al., 2008).
Heavy metal pollutants which compare with other
types of aquatic pollution have been reported to be less
visible, but its effects on the ecosystem and humans are
30 Ayomide Omolara Olofinko, Henry Adefisayo Adewole, Victor Folorunso Olaleye
Agraarteadus : Journal of Agricultural Science XXIX 2018 29–40
intensive and very extensive due to their toxicity and
their ability to accumulate in the aquatic organisms
(Svobodova et al., 2004). Heavy metals when present
in the water accumulate in tissues and organs of aquatic
organism to a level that might affect their physiological
state especially fish and thereby incorporated into food
chain (Akan et al., 2012; Ekpo et al., 2013).
Fish are nutritious and essential food items which
provide high-quality protein, vitamins, minerals and
omega-3 fatty acids (which have been associated with
health benefits due to their cardioprotective effects)
(Wim et al., 2007; Gamal, Shamery, 2010). Despite the
many health benefits associated with fish in a diet, there
are also some health risks related to fish consumption,
mainly due to potential adverse effects of heavy metal
contamination (Mansour, Sidky, 2002).
The accumulation of heavy metals within fish varies
with route of uptake, type of heavy metal, species of
fish concerned, physiology and metabolism (Olatunji,
Osibanjo, 2012; Amita et al., 2012). The exposure of
fish and other aquatic organism to heavy metals in
aquatic environment has also been shown to be a
function of the concentration of the dissolved metals in
the water bodies. Multiple factors including season,
physical and chemical properties of water have also
been reported to play a significant role in metal
accumulation in different fish tissues (Hayat et al.,
2007). The accumulation of these contaminant residues
may ultimately reach concentrations hundreds or
thousands of times above those measured in the water,
sediment and food (Goodwin et al., 2003; Osman et al.,
2007). For this reason, monitoring fish tissue
contamination serves as an early warning indicator of
related water quality problems (Barak, Mason, 1990;
Mansour, Sidky, 2002), enables detection of toxic
chemicals in fish that may be harmful to consumers,
and ensure appropriate action to protect public health
and the environment (Adefemi et al., 2008).
Fish is an important component of the human diet in
Ejigbo and its environs, most of which are sourced for
in Osinmo Reservoir, Ejigbo, Southwestern, Nigeria.
Several studies have been done on Osinmo reservoir
(Adewumi et al., 2014; Adedeji et al., 2015), but heavy
metals bio-accumulation potential in the organ and
tissue of the tilapiine species in Osinmo reservoir have
not been reported. This study, therefore, intends to
determine the concentration of heavy metals in the
water and fillets of the tilapiine species from Osinmo
reservoir and establish the fish-human consumption
safety.
Materials and methods
The Study Area
The study was carried out on Osinmo Reservoir,
Ejigbo, Southwestern, Nigeria. The reservoir was a
man lake that was created by the impoundment of Ataro
River in 2005 primarily to supply potable water. It also
provides a number of ancillary benefits among which is
the production of fish to the surrounding communities.
The reservoir basin extends in length from Latitude
07°52.8' N to 07°53.2' N and in width from Longitude
004°21.2' E to 004°21.7' E (Figure 1). The reservoir has
a surface area of about 0.78 km2 with a mean depth of
3.2 meters (Komolafe, Arawomo, 2008).
Figure 1. (A) Map of Nigeria showing Osun State, (B) Map of Osun State showing Ejigbo Local Government, (C) Map of Ejigbo Local Government (D) Osinmo reservoir. The map of the study area showing the sampling points
Sample Collection Water sampling. Surface water samples were
collected monthly for a period of 6 month (July–
December 2015) from three points in the study area: the
transition, open water and lacustrine area of the
reservoir which was designated as Station A, B and C
respectively (Figure 1). Two litres polyethene bottles
washed with 5% nitric acid rinsed with distilled water
and dried in an oven were used for the collection of
water samples. At each sampling point, the bottles were
rinsed three times with the reservoir water before the
collection of the water sample. The water samples were
then transported to the laboratory where they were
filtered with Whatman filter paper No 42. The filtrate
were then acidified with 2 ml concentrated HNO3 per
litre of filtered water to minimize precipitation and
adsorption to container's wall. The water samples were
then stored for digestion and heavy metal analysis.
Fish sampling. The Tilapia species used for this
study were caught from Osinmo Reservoir with the
help of local fishermen fishing on the Reservoir Area.
Specimen of the fish species collected monthly for a
period of 6 months between July to December 2015 and
identified using identification keys prepared by
(Adesulu, Sydenham, 2007) were those of Oreochro-
mis niloticus, Sarotherodon galilaeus and Tilapia zillii.
The fish specimens were transported to the Fish Culture
Laboratory, Department of Zoology, Obafemi
Awolowo University, Ile-Ife, Nigeria in an ice chest for
further processing.
Fish Preparation. In the laboratory, the specimens
were cleaned by rinsing with distilled water to remove
debris, plankton and other external adherents. Morpho-
metric measurements of the fish specimens were taken
by metric ruler (in centimetres) for the total length and
standard length while the weight of the fish specimens
A
B
C D
Comparative assessment of selected heavy metal load in three tilapiine species inhabiting Osinmo reservoir, Southwestern Nigeria 31
Agraarteadus : Journal of Agricultural Science XXIX 2018 29–40
were measured using a Metler balance (Model P1210)
and values recorded (to the nearest gram). The fishes
were then descaled and the fillets of the fish specimen
were dissected out, weighed and dried using Gallen-
kamp hotbox oven (Model DHG-9030A) at a tempera-
ture 60 °C for 24 hours. After drying, the samples were
pulverised in clean ceramic mortar and pestle and kept
in a well labelled universal specimen bottle prior to
digestion for heavy metal analysis.
Heavy metal determination. Water sample and 2 g
of pulverized fish sample were digested following the
method of Ademoroti (1996). The levels of lead, zinc,
chromium, iron and cadmium of digested samples were
then read using an ALPHA 4 ChemTech Analytical
(serial number 4200) Atomic Absorption
Spectrophotometer (AAS) (Buck Model 205).
Statistical Data Analysis. The data obtained were
subjected to one-way analysis of variance (ANOVA)
and significant differences accepted at P ≤ 0.05 (Zar,
2001). Where significant differences were recorded, the
mean values were separated using post-hoc Tukey’s
(HSD) test. Descriptive statistics for all collected data
were also obtained using SPSS software package
Version 21.
Results
Heavy Metals Concentrations of the Water
Samples Collected from Osinmo Reservoir
The mean concentrations of some heavy metals
assayed in the water samples collected from Osinmo
Reservoir is shown in Table 1. Analysis showed that
zinc had significantly higher concentration out of the
heavy metals assayed, followed by iron and chromium
respectively (Table 1).
Table 1. Post-hoc multiple comparison (Duncan) of the selected heavy metal mean concentration (µg l-1) in the water sample collected from the sampled stations
Heavy metals Station A Station B Station C
Lead 16.50 ± 0.99a 21.17 ± 1.51b 13.83 ± 0.87 a
Chromium 20.17 ± 2.55a 33.17 ± 2.77b 20.00 ± 2.25 a Zinc 254.17 ± 9.35b 197.00 ± 15.77 a 204.67 ± 9.39 a
Iron 39.33 ± 2.63 a 66.83 ± 2.50b 38.00 ± 3.93 a Cadmium 19.17 ± 0.95 a 20.50 ± 2.22 a 24.33 ± 2.44 a
Row means with the same superscript are not significantly different
(P > 0.05) from each other.
Zinc concentration in Station A was found to be
significantly higher (P < 0.05) than that in Stations B
and C. The highest mean concentration of Pb, Fe and
Cr were recorded in water samples collected from
Station B, while Station C had the lowest concentration
of Cd, Pb, and Fe. In station A, Zn had the highest
concentration followed by Fe, Cr, and Cd respectively.
The concentrations of Pb, Cr, and Fe were significantly
higher (P < 0.05) in Station B than at the other two
sampled Stations (Table 1). Although there was
variations in the Cd levels between the three Stations,
there was no significant difference (P < 0.05) between
the three Stations (Table 1). Irrespective of the month
of study, Zn had the highest concentration out of all the
elements assayed followed by Fe, Cr, Cd, and Pb in that
order. In Station A, the order of heavy metal
concentration was Zn > Fe > Cr > Cd > Pb, while in
Station B, the order of heavy metal concentration was
Zn > Fe > Cr > Pb > Cd. For Station C, the order of
heavy metal concentration in the water samples
analysed was Zn > Fe > Cd > Cr > Pb (Table 1).
Monthly mean variation of the heavy metal
concentration in the water sample collected from
Osinmo Reservoir
Lead (Pb). The monthly variation in the Pb+
concentration in the water samples collected from the
different sampled stations during the period of study
(Figure 2) revealed that the level of the element in
station A ranged between 13.00 µg l-1 (July 2015) and
20.00 µg l-1 (November 2015). In Station B, the
concentration varied between 16.00 µg l-1 (July 2015)
and 26.00 µg l-1 (December 2015). In Station C
however, lead concentration monitored ranged between
11.00 µg l-1 (September 2015) and 16.00 µg l-1 (August
and November 2015). Comparative monthly variation
in the water mean Pb+ concentration between the
sampled stations as shown in Figure 2 revealed a
bimodal pattern of Pb concentration with peaks in
August and November (2015) in Stations B and C
during the period of study. In Station A, however, a
peak concentration which occurred in August 2015 was
followed by a drop in the element concentration in
September which was subsequently followed by a
steady increase in concentration up to December 2015.
Figure 2. The monthly mean variation of lead ion concentration (± SEM) in the water samples collected from Osinmo reservoir
Cadmium (Cd). The mean cadmium concentration
in water sample collected from Osinmo Reservoir
during the study period ranged between 15.00 µg l-1
(Station B, July and September 2015,) and 31.00 µg l-1
(Station C, November 2015) (Figure 3). The highest
level of Cd ion (31.00 µg l-1) and lowest level of Cd ion
(15.00 µg l-1) was recorded in Station C in the month of
September and October 2015, respectively (Figure 3).
A bimodal pattern of Cd+ concentration was recorded in
all the sampled stations during the period of study. In
Stations A and B, peak concentrations of Cd+ were
recorded during the months of August and October
2015, while the least concentration was recorded in
September 2015. In Station C however, peak concent-
rations of the element occurred in September and
0
5
10
15
20
25
30
JUL AUG SEPT OCT NOV DEC
Lead
(µ
gl-
1)
Months (2015)
A B C
Sampled Stations
32 Ayomide Omolara Olofinko, Henry Adefisayo Adewole, Victor Folorunso Olaleye
Agraarteadus : Journal of Agricultural Science XXIX 2018 29–40
November 2015. The lowest Cd concentration was
recorded in October 2015 (Figure 3).
Zinc (Zn). The zinc ion levels in the water samples
from Osinmo Reservoir during the period of the study
had the highest value of 288.00 µg l-1 (Station A,
December 2015) and of 144.0 µg l-1 in Station B,
(October 2015) (Figure 4). Analyses showed similar
monthly pattern of variation in zinc concentration in
Stations A and B (Figure 4). The variation in the two
Stations showed a steady increase between July and
September 2015, followed by a decline in the month of
October 2015 subsequently with a steady increase till
December 2015. In Station C, a peak concentration
(224.00 µg l-1) in August, 2015, was followed by a
decline in concentration until the month of October,
2015, before an increase which culminated in the
highest concentration (241.00 µg l-1) of the element in
the water samples during the month of December,
2015.
Chromium (Cr). The chromium ion concentrations in
the water samples collected from Osinmo Reservoir
during the period of study ranged between 9.00 µg l-1 in
Station A (October 2015) and 48.00 µg l-1 in Station B,
(December, 2015) (Figure 5). Monthly comparative
analyses of the concentration of the elements between
the sampled stations showed variations between the
stations. In Station C, a steady increase occurred in the
concentration of the element between July and
December 2015. In Station A, however, the increase in
concentration between July and August 2015 was
followed by a decline in concentration up till October
2015, before a peak concentration (26.00 µg l-1) was
recorded in November 2015. In Station B, the slight
increase in concentration of Cr2+ between July and
August 2015 was followed by a declining concentration
between August and September 2015. Subsequently, a
steady increase in concentration occurred before a peak
concentration (48.00 µg l-1) was recorded in December
2015.
Iron (Fe). The mean iron concentration in water
samples collected from Osinmo Reservoir during the
period of study ranged between 25.00 µg l-1 (Station C,
December 2015) and 73.00 µg l-1 (Station C, October
2015) (Figure 6). Comparative analyses of the Fe levels
between the sampled Stations showed that in Station A,
the peak levels of Fe occurred in the months of July and
September, 2015, while the peak concentration of the
element (73.00 µg l-1) was recorded in October 2015 in
Station B. However in Station C, the peak concent-
rations (51.00 µg l-1) of Fe occurred during the month
of July and October 2015. Analyses also revealed that
the lowest concentration of Fe (25.00 µg l-1) in all the
sampled stations occurred during the month of
December 2015 (Figure 6).
Figure 3. The monthly mean variation of cadmium ion concentration (± SEM) in the water samples collected from Osinmo reservoir
Figure 4. The monthly mean variation of zinc ion concentration (± SEM) in the water samples collected from Osinmo reservoir
Figure 5. The monthly mean variation of chromium ion concentration (± SEM) in the water samples collected from Osinmo reservoir
Figure 6. The monthly mean variation of iron ion concentration (± SEM) in the water samples collected from Osinmo reservoir
0
5
10
15
20
25
30
35
40
JUL AUG SEPT OCT NOV DEC
Cad
miu
m (
µg
l-1)
Months (2015)
A B C
Sampled Stations
0
50
100
150
200
250
300
350
JUL AUG SEPT OCT NOV DEC
Zin
c (
µg
l-1)
Months (2015)
A B C
Sampled Stations
0
5
10
15
20
25
30
35
40
45
50
JUL AUG SEPT OCT NOV DEC
Ch
rom
ium
( µ
gl-
1)
Months (2015)
A B C
Sampled Stations
0
10
20
30
40
50
60
70
80
JUL AUG SEPT OCT NOV DEC
Iro
n (
µg
l-1)
Months (2015)
A B C
Sampled Stations
Comparative assessment of selected heavy metal load in three tilapiine species inhabiting Osinmo reservoir, Southwestern Nigeria 33
Agraarteadus : Journal of Agricultural Science XXIX 2018 29–40
Table 2. Length-weight profile of the sampled cichlid fish specimens from Osinmo reservoir during the study period
Family Fish species Total number
examined
Total length (cm)
Mean total length (cm)
Standard length (cm)
Mean standard length ± SEM
(cm)
Weight (g) Mean weight
± SEM (g)
Cichlidae
Oreochromis niloticus 30 16.00–28.00 19.85 ± 2.50 13.00–22.70 15.97 ± 2.04 94.99–421.08 166.90 ± 74.23
Tilapia zillii 30 11.20–26.10 18.14 ± 3.71 9.20–21.50 13.88 ± 3.00 83.80–373.72 151.31 ± 72.97
Sarotherodon galilaeus 30 10.30–25.50 16.23 ± 3.45 8.30–20.80 13.00 ± 2.78 68.29–355.13 128.05 ± 56.50
Fish Composition and Morphometrics
Thirty (30) specimens each of three fish species:
Oreochromis niloticus, Tilapia zillii and Sarotherodon
galilaeus belonging to the family Cichlidae were
assessed for the fillet heavy metal concentration during
the period of study. The total length, standard length
and the weight of the specimens used for the study is
shown in Table 2. In all cases, sub-adults and adult
specimens of the three species were analysed for the
heavy metal content.
Heavy Metals Concentrations in the Fillet of the
Fish Specimens
The concentration of the heavy metals assayed in the
fillet of the three cichlid species studied is shown in
Table 3. Irrespective of the species, Zn has the highest
concentration in the fish fillet while Cd concentration
was the least. In the species, the order of concentration
was Zn > Fe > Cr > Pb > Cd. Generally, the levels of
the assayed heavy metals were higher in O. niloticus
while the least concentration occurred in S. galilaeus.
The only exception was Fe where the least
concentration was recorded in the fillet of T. zillii.
Comparative analyses between the cichlid species
showed that the highest Zn concentration was recorded
in the fillet of O. niloticus. Statistical analyses revealed
that the concentration of Zn was significantly higher
(P < 0.05) in the fillet of O. niloticus than in the fillet
of T. zillii and S. galilaeus whose concentration were
however found not to be significantly different
(P > 0.05) from each other.
Table 3. Post-hoc multiple comparison of the assayed heavy metals concentration (µg g-1) in the fillets of the fish specimens in mean and ± SEM
Heavy metals O. niloticus T. zillii S. galilaeus
Lead 12.61 ± 0.81b 10.00 ± 0.81a 9.94 ± 0.81a
Chromium 18.44 ± 1.63a 18.22 ± 1.63a 11.67 ± 1.63b
Zinc 190.06 ± 4.20b 175.22 ± 4.20a 168.22 ± 4.20a Iron 36.67 ± 2.41a 14.56 ± 2.41b 31.00 ± 2.41a
Cadmium 8.33 ± 0.46b 6.83 ± 0.46a 5.94 ± 0.46a
Row means with the same superscript are not significantly different (P < 0.05) from each other.
The concentration of Fe which was also highest in the
fillet of O. niloticus was not significantly different
(P > 0.05) from those of S. galilaeus but was
significantly higher (P < 0.05) than the concentration of
the element in the fillet of T. zillii. The levels of Cr in
the fillet of O. niloticus and T. zillii were not
significantly different (P > 0.05) from each other but
the levels were found to be significantly higher
(P < 0.05) than in the fillet of S. galilaeus. Relatively
trace amounts of Pb and Cd recorded in the fillet of T.
zillii and S. galilaeus were found not to be significantly
different (P > 0.05) from each other. However, the
levels of the two elements in the two species were
found to be significantly lower (P < 0.05) than in the
fillet of O. niloticus (Table 3).
Monthly Variation in the Fillet Heavy Metals
Concentration
Lead (Pb). The monthly variation in the Lead
concentration of the fillet of the cichlid species
examined during the period of study is shown in Figure
7. Irrespective of the month of sampling, similar pattern
of concentration of the element was recorded in O.
niloticus and T. zillii specimens caught. However, the
level of Pb was higher in O. niloticus for each
corresponding month. In O. niloticus and T. zillii fillet,
higher concentrations of Pb (15.33 ± 5.03 and 13.00
± 3.00 µg g-1 respectively) were recorded during the
month of November 2015. In S. galilaeus, the lowest
fillet Pb concentration (6.33 ± 3.21 µg g-1) was
recorded during the month of July (2015), while the
highest level (12.33 ± 4.51 µg g-1) was recorded in
December (2015). In S. galilaeus, the level of Pb rose
steadily in the fish fillet sample between July and
September (2015) before a decline in October (2015)
which was subsequently followed by a steady increase
until December 2015 (Figure 7).
Figure 7. Monthly variations in the lead concentration (±SEM)
of the fillet of the fish species caught during the study period (ON – Oreochromis niloticus, TZ – Tilapia zillii, SG – Sarotherodon galilaeus)
Chromium (Cr). The level of chromium in the fillet
of the three tilapiine species studied is shown in Figure
8. Analyses showed that although the level of the
element varied between the species, between July and
August 2015, T. zillii had the highest elemental fillet
level (28.67 ± 10.60 µg g-1) while S. galilaeus had the
least (6.33 ± 3.21 µg g-1). In O. niloticus and
S. galilaeus, the levels of Cr in the fillet of the fishes
were relatively stable between August and October
2015, before a steady increase was recorded between
October and December 2015. In T. zillii, however, the
0
2
4
6
8
10
12
14
16
18
JUL AUG SEP OCT NOV DEC
Lead
(µ
gg
-1)
Months (2015)
ON TZ SG
34 Ayomide Omolara Olofinko, Henry Adefisayo Adewole, Victor Folorunso Olaleye
Agraarteadus : Journal of Agricultural Science XXIX 2018 29–40
lowest Cr concentration (12.33 ± 3.51 µg g-1) was
recorded in September 2015 while the highest
concentration (28.67 ± 10.60 µg g-1) occurred in the
fillet in November, 2015.
Zinc (Zn). The monthly variation in the level of zinc
in the fillet of the studied cichlid species is shown in
Figure 9.
Analyses showed the concentration of the element in
the three species varied within a narrow amplitude. The
highest zinc concentration (220.33 ± 20.50 and 205.00
± 42.79 µg g-1) in the fillet of O. niloticus and
S. galilaeus specimens respectively was recorded in
October 2015 while in T. zillii, the highest
concentration (180.00 ± 5.00 µg g-1) of the element
occurred in September 2015. The least zinc
concentration (121.33 ± 16.01 µg g-1) was recorded in
December 2015 in S. galilaeus, 169.67 ± 1.53 µg g-1
T. zillii in November 2015 and 180.00 ± 16.22 µg g-1 in
O. niloticus in September 2015 (Figure 9).
Iron (Fe). The highest fillet Fe concentration
(44.00 ± 18.03 µg g-1) was recorded in O. niloticus
irrespective of the month of sampling while the least
concentration (13.00 ± 3.61 µg g-1) was recorded in
T. zillii. The concentration of Fe in the fillet of T. zillii
between July and December 2015 was relatively stable
(Figure 10). However, in O. niloticus the fish fillet Fe
concentration was found to increase steadily between
July and September 2015 when peak concentration
(44.00 ± 18.03 µg g-1) was recorded before declining
until December 2015. In S. galilaeus specimens, how-
ever, the highest Fe concentration (39.67 ± 9.61 µg g-1)
in the species was recorded in September 2015, while the
least concentration (24.00 ± 12.29 µg g-1) of the element
in the fillet of the fish was recorded in October 2015.
Cadmium (Cd). The monthly concentration of Cd in
the fillet of the three studied cichlid species varied
widely (Figure 11). In T. zillii, the concentration of Cd
increased steadily between July and September 2015
when the peak concentration (11.33 ± 1.15 µg g-1) was
recorded before declining too (2.33 ± 1.53 µg g-1) in
December 2015, when the least concentration was
recorded. The concentration of Cd in S. galilaeus which
increased in the fish fillet between July and August
2015, declined until October 2015 when the least
concentration (3.67 ± 1.15 µg g-1) was recorded. Sub-
sequently, the level of the element increased in the fish
fillet until the maximum concentration (9.00
± 2.65 µg g-1) was recorded in December 2015. The
peak Cd concentration was recorded in July 2015.
However, the concentration of Cd in O. niloticus
declined between August and September 2015. Sub-
sequently, a high concentration (11.33 ± 1.15 µg g-1)
which was recorded in October 2015 was followed by
a steep decline in concentration of the element until
December 2015 when the least concentration (4.00
± 1.00 µg g-1) was recorded.
Figure 8. Monthly variations in the chromium concentration (± SEM) of the fillet of the fish species Caught during the study period (ON – Oreochromis niloticus, TZ – Tilapia zillii, SG – Sarotherodon galilaeus)
Figure 9. Monthly variations in the zinc concentration (± SEM) of the fillet of the fish species caught during the study period (ON – Oreochromis niloticus, TZ – Tilapia zillii, SG – Sarotherodon galilaeus)
Figure 10. Monthly variations in the iron concentration (± SEM) of the fillet of the fish species caught during the study period (ON – Oreochromis niloticus, TZ – Tilapia zillii, SG – Sarotherodon galilaeus)
Figure 11. Monthly variations in the cadmium concentration (± SEM) of the fillet of the fish species caught during the study period (ON – Oreochromis niloticus, TZ – Tilapia zillii, SG – Sarotherodon galilaeus)
0
5
10
15
20
25
30
35
0 JUL AUG SEPT OCT NOV DEC
Ch
rom
ium
(µ
gg
-1)
Months (2015)
ON TZ SG
0
50
100
150
200
250
JUL AUG SEPT OCT NOV DEC
Zin
c (
µg
g-1
)
Months (2015)
ON TZ SG
0
5
10
15
20
25
30
35
40
45
50
JUL AUG SEPT OCT NOV DEC
Iro
n (
µg
g-1
)
Months (2015)
ON TZ SG
0
2
4
6
8
10
12
14
16
JUL AUG SEP OCT NOV DEC
Cad
miu
m (
µg
g-1
)
Months (2015)
ON TZ SG
Comparative assessment of selected heavy metal load in three tilapiine species inhabiting Osinmo reservoir, Southwestern Nigeria 35
Agraarteadus : Journal of Agricultural Science XXIX 2018 29–40
Relationship between Heavy Metal Concentration
in Water and Fish Fillets
The relationship between concentration of lead in
water and the fillet samples of the three studied species
is shown in Figure 12. Analyses showed there was a
very high positive correlation between the level of Pb
in the water and fillet samples in O. niloticus
(r2 = 0.8448) and T. zillii (r2 = 0.8943). However, there
was a low correlation (r2 = 0.3255) between the lead
concentration in water and S. galilaeus fillet samples.
The relationship between chromium concentration in
water and fish fillet samples is shown in Figure 13. A
very high positive correlation was recorded between
water chromium levels and the element’s concentration
in the fillet of O. niloticus (r2 = 0.8822) and S. galilaeus
(r2 = 0.8849). Comparatively, a low correlation
(r2 = 0.2991) was obtained between the water
chromium level and the element fillet concentration in
T. zillii. Analysis also showed a very low correlation
between water Zn level and the fillet samples of
O. niloticus (r2 = 0.4247), T. zillii (r2 = 0.0645) and
S. galilaeus (r2 = 0.9395) studied (Figure 14). Analysis
showed a very low correlation between water Fe level
and the fillet samples of O. niloticus (r2 = 0.0003),
T. zillii (r2 = 0.4478) and S. galilaeus (r2 = 0.1255)
respectively (Figure 15). Also, very low correlation
occurred between the water Cd level and the fillet
elemental composition in the three species studied.
Analysis showed the correlation coefficients recorded
between Cd levels in water and fish fillet samples were:
O. niloticus – r2 = 0.7520; T. zillii – r2 = 0.0348 and
S. galilaeus – r2 = 0.1346 (Figure 16).
Figure 12. Relationship between Pb levels in the water and fillet samples of the fish specimens used
Figure 13. Relationship between Cr levels in the water and fillet samples of the fish specimens used
Figure 14. Relationship between Zn levels in the water and fillet samples of the fish specimens used
Figure 15. Relationship between Fe levels in the water and fillet samples of the fish specimens used
Figure 16. Relationship between Cd levels in the water and fillet samples of the fish specimens used
Discussion
Specific Variations in the Level of Selected Heavy
Metals in Osinmo Water Samples Lead concentration in Osinmo Reservoir during the
period of study which recorded a monthly range value
of 11.00–26.00 µg l-1 was similar to the result reported
by Bolawa and Gbenle (2010) from Makoko River and
around Carter Bridge, Lagos State, Nigeria. Lead con-
centrations which were significantly higher in station B
could probably be attributed to increased anthropogenic
activities observed during the period of study such as
the proximity of the stations to the irrigation farming
being practised in close proximity of the reservoir. The
level of lead in the water samples collected from the
reservoir, however, differed from the findings of
Olatunji and Osinbanjo (2012) who reported a higher
0
5
10
15
20
25
JUL AUG SEP OCT NOV DEC
Lead
(µ
gg
-1)
Months (2015)
Water O. niloticus T. zillii S. galilaeus
0
5
10
15
20
25
30
35
JUL AUG SEP OCT NOV DEC
Ch
rom
ium
(µ
gg
-1)
Months (2015)
Water O. niloticus T. zillii S. galilaeus
0
50
100
150
200
250
300
JUL AUG SEP OCT NOV DEC
Zin
c (
µg
g-1
)
Month (2015)
Water O. niloticus T. zillii S. galilaeus
0
50
100
150
200
250
300
JUL AUG SEP OCT NOV DEC
Zin
c (
µg
g-1
)
Month (2015)
Water O. niloticus T. zillii S. galilaeus
0
10
20
30
40
50
60
JUL AUG SEP OCT NOV DEC
Iro
n (
µg
g-1
)
Months (2015)
Water O. niloticus T. zillii S. galilaeus
36 Ayomide Omolara Olofinko, Henry Adefisayo Adewole, Victor Folorunso Olaleye
Agraarteadus : Journal of Agricultural Science XXIX 2018 29–40
range of Lead values of (20.00–40.00 µg l-1) in surface
water of River Niger, Nigeria. Other studies of surface
water from Ikpoba River, Nigeria by Oguzie, Izevbigie
(2009) and Nairobi River, Kenya by Kithiia (2006),
also reported higher mean Lead values of 35.00 µg l-1
and 100.00 µg l-1 respectively which were however
higher than the level of Lead recorded in Osinmo
Reservoir during the period of study. However,
irrespective of the lower values of Lead recorded in the
reservoir, the values were above the maximum
acceptable limit of 10 µg l-1 for potable water (WHO,
2002; 2003). Goel (1997) reported that Lead concent-
ration in natural water increases mainly through anthro-
pogenic activities. Hence, the source of Lead into the
Osinmo reservoir during the period of study will likely
include depositions from soil erosion and run-offs from
agricultural lands within the reservoir catchment areas
(DWAF, 1996). Lower levels of lead recorded in water
samples from station C was probably due to the
minimal pollution activities close to the sampling point.
The general decrease in Lead concentration during the
period of study could also be due to dilution effect from
water during the rainy period as well as absorption of
the element by plants and sediments in the reservoir
(Kithiia, 2006; Kar et al. 2008)
Cadmium concentration in Osinmo Reservoir during
the period of the study which has a mean monthly range
15.00 and 31.00 µg l-1 was higher than the values re-
ported by Ekpo et al. (2013) in Ikpoba River (1.00 and
2.00 µg l-1) in Benin City, Nigeria. The higher levels of
cadmium in the water samples across all the stations of
Osinmo reservoir could be attributed to various anthro-
pogenic activities especially ongoing agricultural
activities in the area. According to Modaihsh et al.
(2004), fertilizers such as phosphate fertilizers and
other types averagely contain 13.4 µg g-1 of cadmium
which tends to accumulate in the soil when fertilizers
are applied annually on farmlands. Some of the
accumulated Cd probably get leached out of the soil and
end up in the reservoir. The cadmium concentration
which increased from July to September in sampling
station C could, therefore, be attributed to such run-offs
from the surrounding soils. The cadmium level in
Osinmo Reservoir during the period of study was
however found to be above the acceptable limit of
5.0 µg l-1 recommended by EPA for portable water
(ATSDR, 1999) and 3.0 µg l-1 recommended by WHO
(1984) and FEPA (2007).
Presence of zinc in water bodies such as Osinmo
reservoir could be associated with human activities
such as the use of chemicals and zinc-based fertilizers
by farmers (Egila, Nimyel, 2002). Zinc ion concentra-
tion in water samples collected from Osinmo Reservoir
during the period of study (with a monthly range value
of 144.00–288.00 µg l-1) was within the recommended
acceptable limit for potable water of 300 µg l-1 (WHO,
2008). Zinc concentrations that were higher than what
was recorded in Osinmo reservoir during the present
study have been reported in other water bodies. Kar et
al. (2008) and Agatha (2010) reported a higher mean
zinc level of 78250 µg l-1 from Forcado River, Nigeria.
Olatunji, Osinbajo (2012) also obtained higher mean
zinc values in the range of (1980.00–4030.00 µg l-1) in
River Niger, North Central Nigeria. Although zinc is
considered to be relatively non-toxic, especially if
taken orally, zinc deficiency has been reported to cause
anaemia and retardation of growth and development
(McCluggage, 1991). Excess amount of the element
has also been reported to cause system dysfunctions
that result in impairment of growth and reproduction
(INECAR, 2000; Nolan, 2003).
Iron concentration in Osinmo Reservoir during the
period of study which recorded a monthly value of
between 25.00 µg l-1 to 73.00 µg l-1 was within the
300 µg l-1 recommended permissible limits in drinking
water (FAO, 1996; FEPA, 2003). During the period of
study, the Fe concentration recorded in water samples
from all stations were, however, smaller than a higher
mean value of 380 µg l-1 recorded in water upstream of
Ikpoba River (Oguzie, Izevbigie, 2009). Analyses
which showed the iron concentration to significantly
higher in station B, however, could be related to the
nearness of the sampled station to an irrigation farming
scheme being practised in close proximity of the
reservoir during the period of study. The decrease
observed in iron concentration between the months of
October to December 2015 across the sampling sta-
tions, on the other hand, might be due to the advent of
the dry season which probably led to higher uptake of
element by the biota. Although the level of iron in water
samples collected from Osinmo Reservoir was below
the maximum acceptable limit of 300 µg l-1 for iron in
portable water (WHO, 1984; FEPA, 2003), the con-
centration of the element in water from the reservoir
was found to be higher than the concentration of other
elements investigated except zinc. The high level of the
element in the water samples could be due to the high
degree of solubility of the ferrous and ferric forms of
iron in water. This could be explained by the fact that
iron being the most abundant in the environment could
conceivably be bio-accumulated more than the other
metals (Oronsaye et al., 2010).
Chromium concentrations in water samples from
Osinmo Reservoir during the sampling period which
ranged between 9.00 µg l-1 to 48.00 µg l-1, were below
the recommended acceptable limits for potable water
which is 50 µg l-1 (FEPA, 2007; WHO, 2008). The Cr
levels recorded were comparatively lower when
compared to the levels of the element reported in other
water bodies. A higher mean chromium level of
49.00 µg l-1 was reported by Oyhakilome et al. (2012)
in Owena multipurpose dam water, Nigeria. Olatunji
and Osinbanjo (2012) also reported much higher mean
chromium levels of 1190 to 3160 µg l-1 in River Niger,
Nigeria. During the period of study, however, the
increase in chromium level between the months of
October and December 2015 could be associated with
the onset of the dry season which probably led to
incremental concentration as the volume of water
reduces in the reservoir.
Comparative assessment of selected heavy metal load in three tilapiine species inhabiting Osinmo reservoir, Southwestern Nigeria 37
Agraarteadus : Journal of Agricultural Science XXIX 2018 29–40
Heavy Metal Levels in the Fish Fillet The mean Lead concentration in the fillet of the
tilapiine species analysed which were 12.61 ± 0.81 µg g-1
in O. niloticus, 10.00 ± 0.81 µg g-1 in T. zillii and 9.94
± 0.81 µg g-1 in S. galilaeus were found to be above the
2.0 µg g-1 recommended acceptable limit for lead in
fish products (FEPA, 2003). Microhabitat utilization,
feeding habits, age, sex and fish species probably
determined the accumulation pattern of the heavy metal
in the fishes (Kotze, 1997). The results obtained during
the study however closely agreed with Okoye (1999)
who reported mean values of 9.00 µg g-1 for lead in
fishes collected from the Lagos Lagoon. The values
obtained during the period of study were higher when
compared to the reported values of (0.395–0.62 µg g-1)
by Doherty et al. (2010) in fishes collected from Lagos
Lagoon. Bolawa and Gbenle (2010) also reported hig-
her mean values of the element which ranged between
31.00 and 65.00 µg g-1 in fishes collected from Makoko
River and Carter River in Lagos, Nigeria. Farombi et
al. (2007) on the other hand, reported the Lead values
of between 0.73 to 4.12 µg g-1 in C. gariepinus
collected from Ogun River while Obasohan et al.
(2006) reported a mean range values of 0.10 to
0.83 µg g-1 in some fishes from Ogba River, Nigeria.
Zinc which is an essential microelement required for
numerous aspects of cellular metabolism occurs
naturally in organisms and in the earth crust. The mean
zinc concentration in the fillet of the fish species
assayed were 190.06 ± 4.20 µg g-1 in O. niloticus,
175.22 ± 4.20 µg g-1 in T. zillii and 168.22 ± 4.20 µg g-
1 in S. galilaeus. These values were found to be below
the recommended acceptable limit of 2000–
13 000 µg g-1 (WHO, 2003). The order of zinc
concentration in the fish species caught from Osinmo
reservoir were S. galilaeus < T. zillii < O. niloticus. Fish
has been reported to accumulate zinc from both the
surrounding water and from their diet (Eisler, 1993).
Although, zinc is an essential element, at high
concentration it has been reported to be toxic to fish,
causing mortality, growth retardation and reproductive
impairment (Sorenson, 1991). Oluseye et al. (2012)
reported a much lower mean values of zinc
concentration (0.690 µg g-1) in fish species caught in
Dandaru Reservoir, Ibadan, when compared with those
of the studied tilapiine species caught in Osinmo
reservoir. Akan et al. (2012) also recorded a much
lower mean zinc value in the range of 0.15 to 0.25 µg g-
1 in fishes caught from River Benue in Adamawa,
Nigeria when compared with the zinc levels in the
studied cichlids during the period of study. However, a
higher mean value of 158.30 µg g-1 was reported for
fishes caught in Jakara River, Kano State (Ibrahim,
Said, 2010). The concentration of zinc in O. niloticus
which was significantly higher than in the other two
cichlid fish species could probably be diet related. O.
niloticus has been considered as a benthic omnivore
feeds on benthic crustaceans and sessile molluscs and
occasionally preying on other smaller fishes (Orban et
al., 2008). The higher value of the element in the fish
probably confirmed Ney and Van Hassel (1983) earlier
observation that lead and zinc concentration were
expected to be higher in benthic fishes.
The mean cadmium concentration in the fillet of the
tilapiine fish species from Osinmo reservoir assayed
which respectively were: 8.33 ± 0.46 µg g-1 in O. nilo-
ticus, 6.83 ± 0.46 µg g-1 in T. zillii, 5.94 ± 0.46 µg g-1
in S. galilaeus were above the recommended acceptable
limit of 1.0 µg g-1 (Egila, Nimyel, 2002). Although
cadmium occurs naturally in the environment, the
accumulation of cadmium in fish samples could be as a
result of agricultural activities such as land preparation,
application of agrochemicals and other activities.
According to Rashed (2001), Pb and Cd concentrations
are known to increase in fish tissues collected in
freshwater ecosystem impacted by agricultural
activities. Thus, there is the possibility of these heavy
metals emanating from the chemical fertilizers,
weedicides and all forms of pesticides being utilized in
the cultivation of farms within the reservoir catchment
area. Comparatively, Ibok et al. (1989) reported lower
cadmium values of 0.24 and 0.45 µg g-1 in P. Obscrura
and Hemichromis fasciatus caught in some streams in
Ikot Ekpene area of Nigeria. Abdulrahman and Tsafe
(2004) on the other hand reported a slightly higher
value of cadmium in fishes caught from Sokoto Rima
River which was attributed to agrochemical usages.
Kidwell et al. (1995) however observed that predatory
fish species accumulated more mercury while the
benthivores contained higher concentrations of
cadmium and zinc. Bolawa and Gbenle (2010) reported
a comparatively higher cadmium value of 23 to
90 µg g-1 from Makoko River and Carter Bridge River
in Lagos, Nigeria, when compared with those of
tilapiine species from Osinmo reservoir. However,
Ekpo et al. (2013) reported a much lower mean
cadmium value in the range of 1.00 to 2.00 µg g-1 in
fishes caught from Ikpoba River, Benin City, Nigeria.
The higher concentration of cadmium in fish fillets
during this study especially in O. niloticus could be due
to their ability to tolerate very high levels (14.8 mg l-1)
of waterborne cadmium (Garcia-Santos et al., 2006).
The mean iron concentration in the fillet of the three
tilapiine fish species analysed during the period of study
which were 36.67 ± 2.41 µg g-1 in O. niloticus,
14.56 ± 2.41 µg g-1 in T. zillii and 31.00 ± 2.41 µg g-1 in
S. galilaeus respectively were below the 300 µg g-1
acceptable recommended limits for iron in food (FAO,
1996; FEPA, 2003). The levels of iron in the fillet of the
three tilapiine species during the period of study agreed
with values of between 51.32–107.54 µg g-1 reported by
Obasohan (1997) in the fillet of fish species collected
from Ogba River, Benin City, Nigeria. Although
agricultural activities could have contributed to the
concentration of iron in the fish fillet samples, the
primary source of iron in the fillet could likely be the
naturally occurring iron present in the soil (NRC, 1989).
Also, the haemoglobin component of the blood which is
iron-based is also probably a major contributor of the
iron level in the fillet of the fishes (Camara et al., 2005).
38 Ayomide Omolara Olofinko, Henry Adefisayo Adewole, Victor Folorunso Olaleye
Agraarteadus : Journal of Agricultural Science XXIX 2018 29–40
Chromium is an essential trace element in human but
in excesses, it could have lethal effect on fish and
wildlife (Robertson et al., 1992). The mean chromium
concentration in the fillet of the fish species analysed
were 18.44 ± 1.63 µg g-1 in O. niloticus, 18.22 ±
1.63 µg g-1 in T. zillii, and 11.67 ± 1.63 µg g-1 in
S. galilaeus. The values of the element recorded in the
fillet of the various tilapiine species during the period
of study were found to be within the acceptable limit of
50 µg g-1 recommended for fish and fish products
(WHO, 1984; FEPA, 2007). However, the consumption
of fish from the reservoir should, however, be done
with caution as cumulative effects of the element might
constitute health hazards to aquatic life as well as man
who feeds on the fishes (Oronsaye, 2010). Ugwu et al.
(2012) had earlier reported a much higher chromium
level (56.00 µg g-1) in muscles of O. niloticus obtained
from River Usuma, Nigeria. Agricultural activities such
as application of agro-chemical like fertilizers and
pesticides utilized within the reservoir catchment basin
could be fingered as the source of chromium in the fish
sample.
Conclusion
The study concluded that the elevated levels of lead
and cadmium in the water and the fish fillet samples
assayed indicated that the two elements negatively
impacted the fish fillet quality, thereby raising human
health consumption safety issues.
Conflict of interest
None of the authors has any potential conflict of interest
related to this manuscript.
Author contributions
V.F. Olaleye designed the experimental frame work and
critically reviewed the manuscript for final submission
A.O. Olofinko: Data collection, analyses and interpretation were
done by the author
H.A. Adewole: This author assisted in the analysis and
interpretation of some of the data, and also draft the manuscript
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